Electric motors are well known in the art and have been placed into use in a variety of applications, including the handling of air. In this circumstance, an electric motor is coupled to a fan by a rotating shaft, creating a motor-fan unit, which produces a flow of air as needed. For example, the motor-fan unit may be used to generate working air for vacuum-type devices, such as vacuum cleaners, utility vacuums, as well as other devices that operate in environments that are dry, or that have varying degrees of moisture. One particular type of motor-fan unit is referred to as a bypass discharge-type motor-fan unit and operates such that working air is moved by the fan unit to create a vacuum that draws debris and liquid entrained air into the fan unit, while a separate cooling fan pulls cooling air into the motor unit to keep it cooled. Due to this operation, bypass discharge-type motor-fan units are configured such that the motor unit receiving the cooling air is separated from the fan unit generating the working air by a plate or other partition. This plate or partition provides an aperture or other interface to allow the shaft maintained by the motor unit to extend therethrough so as to rotate the fan. Unfortunately, during operation of the motor-fan unit, the liquid entrained in the working air tends to penetrate the area of the partition through which the shaft extends. As a result, water, detergents, and other liquid is permitted to come in contact with one or more bearings that carry the rotating shaft of the motor unit, causing it to become degreased, which may contribute to the premature failure of the motor unit. In addition, liquid and debris that penetrates into the region of the motor unit may cause the electrical components of the system to be damaged, causing the motor unit to fail.
In response to this problem, techniques have been developed, which utilize various arrangements of seals to prevent liquid and other debris from entering the motor unit around the portion of the shaft that extends through the partition. However, such techniques are inefficient, and do not provide a commercially acceptable level of performance. For example, air seals have been used in the past to provide a seal about the portion of the shaft of the motor unit that extends into the fan unit. These air seals generate a vacuum to evacuate liquid that has penetrated into the vicinity of the air seal. Unfortunately, such air seals generate an insufficient amount of vacuum pressure, and thus are generally ineffective in thoroughly evacuating liquid and moisture from about the shaft carrying bearing and the electrical components maintained by the motor.
Therefore, there is a need in the art for a bypass discharge-type motor-fan unit that utilizes a labyrinth seal that is disposed about a rotating shaft of the motor unit to prevent liquid from penetrating through the fan unit and into the motor unit. In addition, there is a need for a bypass discharge-type motor-fan unit that maintains a rotating shaft that includes a vacuum bore to evacuate liquid that enters an evacuation zone. Furthermore, there is a need for a bypass discharge-type motor-fan unit that rotates a fan via a shaft to generate a negative-pressure region proximate a vacuum bore maintained by the shaft so that liquid that has entered an evacuation zone can be evacuated by the vacuum generated within the vacuum bore.